In various mechanisms for transmitting rotational torque, end portions of two rotational shafts require a coupling assembly for common rotation of the shafts. In an internal combustion engine, the engine or an electric motor can drive the input shaft which can transfer rotational torque to drive an output shaft. Assembling the input and output shafts require effort and precision in axial alignment of the input and output shaft having separate longitudinal axes for transmitting a maximum amount of rotational torque between the members. Coupling the input and output shaft can also result in radial and angular misalignment or clearances between the rotating shafts. Currently used coupling assemblies can include flexible members such as springs, rubber pieces, or the like. Known flexible couplings are disclosed in U.S. Pat. Nos. 7,641,557; 6,500,071; 6,325,722; 5,700,197; 4,897,073; and E.P. Patent No. 1,064,468.
In many cases in an internal combustion engine, it is desirable to assemble the two shafts without any secondary assembly operations such as tightening a collar around one of the shafts. A spline coupling is commonly used to simplify assembly. In a spline coupling, one shaft includes an external spline, and the other shaft includes an internal spline. Assembly is achieved by mating the internal and external splines. Limitations of a spline coupling include cost of creating the splines on the shafts, backlash in the splines coupling that results in increased noise, vibration, and harshness as well as increased shock loading under reversible torques. Misalignment of the spline coupling may reduce its strength or produce excessive reaction loads on the mating shafts. Another method of assembling an input shaft to an output shaft involves using a tapered fit, sometimes with extra features to increase torque capacity of the coupling. However, such devices again can be expensive to manufacture and require an additional axial force to keep pressure on the tapered surface. To accommodate misalignment, such couplings can include a flexible member such as a bellows or beam coupling.